Resin consolidated sandpack

ABSTRACT

In sandpacking a cased and perforated well completed into an unconsolidated reservoir, a slurry of sand grains that are coated with a self curing epoxy resin formulation is pumped into the well by a procedure that ensures the filling of perforations and formation voids with a mass of resin-coated sand which will consolidate downhole and subsequently be drilled out to leave the interior of the casing free of obstructions.

United States Patent Waid 1451 Oct. 10, 1972 [54] RESIN CONSOLIDATED SANDPACK [72] Inventor: J. M. Waid, Houston, Tex.

[73] Assignee: Shell Oil Company, New York, NY.

[22] Filed: Feb. 3, 1971 [21] Appl. No.2 112,191

[52] US. Cl ..166/276, 166/290 51 int. Cl. ..E2lb 43/04 58 Field 61 Search ..166/276, 278, 290, 29s

[5 6] References Cited UNITED STATES PATENTS 2,288,556 6/1942 Vollmer ..166/276 2,674,323 4/1954 Cardwell 166/276 2,941,594 6/1960 Ladd et al 166/276 2,986,538 5/1961 Nesbitt et a1 ..-...l66/276 X 3,489,222 l/1970 Millhone et a1 l 66/ 290 3,621,915 11/1917 Bruist et a1. ..166/276 Primary ExaminerStephen J. Novosad Attorney-H. W. Coryell and Harold L. Denkler [5 7] ABSTRACT In sandpacking a cased and perforated well completed into an unconsolidated reservoir, a slurry of sand grains that are coated with a self curing epoxy resin formulation is pumped into the well by a procedure that ensures the filling of perforations and formation voids with a mass of resin-coated sand which will consolidate downhole and subsequently be drilled out to leave the interior of the casing free of obstructions.

10 Claims, 3 Drawing Figures RESIN CONSOLIDATED SANDPACK BACKGROUND OF THE INVENTION The invention is a well treatment for providing a resin consolidated sandpack within a well that was completed in an unconsolidated reservoir by means of casing and perforating equipment and techniques. The present invention is particularly useful as a remedial treatment for filling voids and replacing sand that was removed from the reservoir formation while fluid was being produced from the well.

Many wells are cased and perforated within unconsolidated reservoirs. In such wells, the inflowing of sand into the well conduits is a serious problem and may lead to a loss of the well. Where sand inflows have occurred voids are left within the reservoir formation. If the voids are left open, the formation is weakened and may collapse even though a sand consolidation treatment has been employed to consolidate the reservoir formation in the vicinity of the perforations.

It is known that such voids in unconsolidated reservoirs can be repacked by injecting a slurry of sand in a liquid that carries the sand through the perforation tunnels and into the voids, where it is screened out against the face of the reservoir formation. Such a transportation of sand into the voids is accompanied by the deposition and piling up of a mass of sand within the casing, where some of the liquid remains static and the sand settles out of suspension.

In a conventional sandpacking process, sand grains are coated with an uncured resin that is subsequently cured when contacted by a catalyst. A slurry of such coated grains is pumped into the well. The sand which is deposited within the casing is removed by a liquid circulating sand removing operation. Then, fluid containing a catalyst is injected in order to initiate the curing of the resinous material on the sand grains. In such a sand removing operation, a string of tubing is usually extended within the casing to a depth near the top of the sand, fluid is pumped into the well through the casing annulus (i.e., the space between the casing and the tubing) while sand-laden fluid is flowed out of the well through the tubing and the tubing is lowered to keep its lower end near the top of the sand. During such an operation, unconsolidated sand in the perforations and voids tends to be removed, for example, due to the backflowing of the sand carrier fluid from locations within the reservoir formation into which it was injected at a relatively high pressure in order to ensure that the sand was transported through the perforations and into the voids.

SUMMARY OF THE INVENTION In accordance with this invention a cased and perforated portion of a well completed into an unconsolidated reservoir is sandpacked by the following combination of steps. Sand grains are coated with a self curing epoxy resin formulation and suspended in a carrier liquid. The suspension is pumped into the well through tubing extending to a point of discharge near the lowest perforation. Each time the perforated casing and the adjacent voids have become filled with a mass of deposited sand extending up to the depth of the point of discharge, the point of discharge is raised, until the sand deposits extend above the highest perforation. The pumping in of suspension is then stopped and the resinous coating on the sand grains is allowed to cure. The interior of the casing is subsequently drilled free of the consolidated mass of sand which is formed within the casing, throughout the length of the perforated interval.

In a particularly suitable procedure, the present invention is conducted by:

l. Mechanically isolating the perforated interval from an inflow of fluid standing within the borehole and placing a sand consolidating resin-compatible fluid in the perforated portion of casing and adjacent portions of earth formation.

2. Installing (or arranging) a conduit so that it extends from a surface location to the perforated interval and is adapted to be lengthened or shortened to position the bottom of the conduit at different depths within the perforated interval.

3. Forming a slurry of sand grains that are coated with resin-forming material and suspended in a liquid and pumping into the conduit an amount of slurry that contains sufficient sand grains to refortify the formation (by replacing produced formation sand with resincoated sand) and fill the perforated interval of the easing from below the lowest perforation to a point above the uppermost perforation (but below the location of the device, such as a squeeze packer, by which the perforated interval is mechanically isolated).

4. Displacing the slurry from the lower end of the conduit while it is located near the bottom perforation and raising end of the conduit at a rate such that the packing of the formation and the settling of sand grains in the borehole at each of a succession of depths within the perforated interval is indicated by a decrease in the fluid injectivity (which causes a corresponding surface pressure increase, when the rate of inflow is constant); and

5. After allowing the resin-forming material to solidify, drilling through the consolidated sand and that has formed within the well casing, so that the borehole is unobstructed.

DRAWINGS FIG. 1 is a schematic partially cross-sectional illustration of a cased and perforated interval of a well borehole equipped for practicing the present invention.

FIG. 2 is a similar illustration at a later stage of operating the present process.

FIG. 3 is a similar illustration of an enlarged portion of the casing and perforation tunnels within such an interval.

DESCRIPTION OF THE INVENTION FIG. 1 shows well bore 2 containing casing 3 surrounded by a sheath of cement 4. The casing is penetrated by perforations 5 having perforation tunnels extending from the borehole interior 7 to a surrounding unconsolidated reservoir 8. The perforated interval of borehole is isolated from an inflow of fluid standing in upper portion 7 a borehole interior by packing means 9 (such as a standard squeeze packer) surrounding pipe string 10.

Tubing string 12 is extended through pipe 10 to provide a conduit arranged to extend between a surface location and any of a series of depths within the isolated interval of the borehole. Tubing 12 is extended through a sealing means (not shown) such as a hydraulic blowout preventer means near the wellhead in order to maintain a seal across the annular space 13 between tubing 12 and pipe 10 while permitting vertical movement of the tubing 12. Alternatively, a conduit can be arranged to extend between a surface location and various depths within the isolated interval by using an arrangement of pipe string 10 and packer 9 (without tubing 12), that provides an elongated section of external seals along the pipe string 10 (used as tubing) and a polished-bore packer that slideably seals against the external seals so that the pipe 10 can be moved through the packer to position it at various depths within the isolated interval (for example, by means of an Otis Permatrieve Packer).

As known to those skilled in the art, each of the above described well drilling and completion operations can be accomplished by means of various items of commercially available equipment and techniques.

FIG. 1 shows fluid 14, comprising a slurry of resincoated grains, being pumped through and displaced out of the lower end of tubing 12 while it ends near the bottom of the perforated interval of casing. Such a slurry displacement tends to form a turbulent zone near the end of the tubing and insures that the grains remain suspended in fluid and are carried by the fluid that flows through perforations and into reservoir 8 as in dicated by the arrows. Some of the so-injected resincoated grains fall out of suspension forming a sand build-up, in the form of a mass 15, as they settle out of the relatively static portions of the grain suspending fluid within the borehole and some are screened out against the face of the reservoir to form a mass 15 (see FIGS. 2 and 3) as the grain suspending liquid flows into the reservoir.

FIG. 2 shows a later stage of the same process, after tubing string 12 has been raised. The tubing is raised each time the packing of the perforations below the tubing end has caused a sand mass 15 to be built up within the borehole to near the end of the tubing 12. Each time such a build-up occurs, the inflowing fluid is forced to flow through more of the sand mass. This causes a significant reduction in injectivity and, if the fluid is being injected at a constant rate, a surge of greater injection pressure can be detected at the surface location.

In the present process, a slurry conveying conduit, such as tubing 12, is preferably moved up in increments (such as 1 foot increments) that each contain only a few (such as 4) perforations. The movements are preferably spaced to provide a rate slow enough so that the build-up of sand to near the point of discharge at the end of the inflow conduit, causes a reduction in injectivityat each increment. Such an injectivity change indicates that the perforations below the point of discharge have been fully packed with sand and packed sand has built up within the borehole to the end of the inflow conduit. The injection of slurry is preferably continued while the inflow conduit is being raised, but can be interrupted before, during or after each raising of the conduit, if necessary.

The amount of slurry that is injected is important. It should contain sufficient resin-coated sand to replace produced formation sand with resin-coated sand and to fill the interior of the borehole from below the bottom perforation to above the top perforation, without extending into contact with the packing device used to isolate the perforated interval. The volume of theliquid into which such an amount of resin-coated sand grains are suspended can be varied to accommodate the viscosity of the suspending liquid, the slurry density capabilities of the slurry pumping devices, etc.

The present process is particularly suited for use in wells from which sand has been produced, such as those receiving a remedial treatment. The amount of sand needed to fill a length of casing equalling the perforated interval should be increased by an amount sufficient to replace the produced sand. The exact amounts of such increases will vary depending upon the reservoirs but in typical Gulf Coast Miocene fields, such replacement amounts are from about eight to 10 sacks (.100 pound sacks) of the coated sand per foot of perforations from which sand has been produced.

The slurry of resin-coated sand has been displaced through the injection conduit and out its lower end by chasing it with a relatively inert fluid 17, as shown in FIG. 2. The chasing or displacing fluid, or at least the frontal portion of it, is preferably a solid-free hydrocarbon, such as diesel oil.

In comparison with previously proposed types of sand control measures that utilize grain-interbonding resins, the present invention utilizes a relatively limited quantity of resin. In comparison with an in-situ epoxy resin sand consolidation of the reservoir sand, the present process has the advantage of: (l) combining the processes of sandpacking andconsolidating into one step, in contrastto separate steps, and thus providing a saving in rig time (which is particularly valuable in situations in which rig costs are high, such as in offshore locations); and (2) providing key features of sandpacking such as leaving an unrestricted well bore adapted to receive substantially any downhole operations. In addition, and possibly most important, the present process provides a saving (relative to a standard in situ formation sand consolidation with epoxy resin) in which the material costs are reduced by 30 to 50 percentwhile increasing the remedial efficiency and durability of the treatment.

After the resin-forming sand-grain coating materials have been allowed sufficient time to' become hard at the reservoir temperature, well treating equipment items such as the inflow conduit 12, packer 9, tubing string 10, etc., are removed from the well. A drill string assembly such as a rotary drill string containing a bit and scraper are run in and operated to drill out the plug of consolidated sand slurry that is formed within the borehole. This opens the borehole to substantially its full internal diameter while leaving a resin-consolidated, permeable, integral mass of sand in each of the perforations 5 (see FIG. 3) so that voids caused by removal of formation sand while producing the well and the perforation tunnels are filled with the resinconsolidated sand from locations within the casing and the borehole to locations within the reservoir formation.

In a preferred procedure, the 'slurry of resin-coated grains is formed by coating solid granular particles with a solution of an epoxy resin-forming material and amino group containing curing agent dissolved in a liquid polar organic solvent and suspended in a liquid carrier (such as a hydrocarbon carrier) that has a limited solubility that provides a limited partitioning (or partial extraction) of the polar solvent between the resin-forming components and the liquid carrier. Such pack within a cased and perforated interval of a well bore comprising:

positioning within the borehole, means for mechanically isolating the perforated interval from an ina carrier liquid controls the curing or polymerizing rate 5 flow of the fluid Standing Within the borehole;

of the resin-forming components that coat the grains to arranging a conduit to extend from a surface location an extent that can be adjusted so that, und r th to within the borehole so that it can be moved verdownhole temperature conditions, the coated grains i lly from One to a SerleS 0f epths Within Said are interbonded to form a high compressive strength Perforatedmterval;

epoxy resin-coated consolidated sand and/or gravel P p the conduit a slurry, eomphsmg Sand pack. Such an epoxy resin-forming material is one that grams Coated Wlth a Self eul'lhg p y teeth-form contains polyepoxide radicals having a plurality of g materlat and suspended q 118mg ah vicina] epoxy groups and such an amino group containamount Of slurry that contains sufficient grams to ing curing agent is a poly-functional amine having a refortlfy the formatloh y l'eplaelhg the Produced plurality of nitrogen atoms with at least one hydrogen formation sand wlth teeth-coated Sahd and to atom attached to each nitrogen atom. A particularly the casing Wlthlh the Perforated Interval of the suitable liquid carrier is a relatively viscous hydrocarborehole from below the lowest Perforatloh t bon, such as Valvata No. 78 or Valvata No. 79 above the uppermost Perforatloh but below Sald (lubricating oil, available from Shell Oil Company) means for mechanically lsotatlhg the Perforated having a viscosity of 1 35 cp at 72 F. l;

in a preferred procedure for injecting a slurryof dlslplacmg 3 1p g 2 i z the resin-coated sand grains, the slurry is pumped through g i a o if l i the conduit extending between a surface location and ratee s z g g g i fi g z i g the isolated portion of the borehole at a rate that u u e an y ls pu pe o the formation to cause the filling of the borehole generates a fiu1d1zed bed of the coated grams near the with sand rains and a decrease in fluid ctivit end of the inflow conduit at each of at least several loat each succession of de ths within i cations adjacent to relatively short increments within p pe the erforated interval In a articularl referred em rotated Interval; and

b0 (15mm t the slurr is'so ingcted at Fessure that is after allowing said resin-forming material to solidify t y d l f t P b t th on said sand grains, drilling through the con- Su crea e m n: rac a. e ween solidated sand within the borehole.

casllg S f f an surrom mg resegvolr 2. The process of claim 1 in which said sand grains san s,h ut lS ms: icienft to mlitiatel'im pr p are coated with a solution of epoxy resin-forming wrest at exten y mm t 6 E r h 3 5 material and amino group containing curing agent dis- The Present lhvehtleh has been tested Successfully solved in liquid polar organic solvent and the so-coated the field in situations in Wl'llCl'l other sand COllSOhdatlOl'l grains are uspended in hydrocarbon having a meas e e failed have been ated y limited miscibility with said polar organic solvent. perience to be inapplicable. The test conditions and 3. The process of claim 1 in which from about eight results are summarized in Table I. Except where it is to 10 pound sacks of coated sand grains are used otherwise indicated, the sandpacked placement per foot of perforation through which sand has previtechniques and equipment were substantially as ously been produced.

described above. in each case the sand used was coated 4. The process of claim 1 in which said slurry is diswith Eposand l 12. placed into the perforated interval at a rate that creates TABLE I Quantity Perforated of sand interval (100 lb.

(feet) sacks) Placement method Previous well condition Results and conclusions 6 16 Otis Permatrieve Packer w/ZO Sanded up zone on vacuum. Lost Produced trace of sand during first day of testing. No seals; 2% tubing with tailpipe circulation zone. sand thereafter. Cumulative production since iob movement. 93,000 BO plus 139,000 BW. Job execution excellent.

Well now shut in due to casing problems u hole.

a 20 Otis Permatrieve Packer w/ZO' Sand producing well; failed Used revised pumping methods but were una 19 to seals; 2% work string with tail screen and liner, lost circulation underdisplace since zone on vacuum. Made sand pipe movement. zone. but did not stand up.

8 40 Standard squeeze packer with do Ratreatment of previous (above) job to insure sand 1%" work string and tail pipe pack. Got pressure increase indicating packing movement. each time before tail ipe moved. Made trace of sand initially none 1; ereafter. Cumulative productiorii since job is 25,000 130 plus 35,000 BW with S311 5 40 do Sand producing well; failed Treated and produced 3,500 BO plus 46000 BW screen and liner lost circulation before casing holes 11 hole forced zone to he tempzone. Screen and liner tugged orarily abandoned. POSANPAC was successful with rnigratin format on fines. and not related to loss of zone.

3 20 do Failed screen an liner and Well brought in making 1% sand. Sand cleaned up to EPOSAND 9 job. Casing colproduce at rate of 30 BO plus 540 BW. lapse in perforated interval.

3 30 Standard squeeze packer with Stabilized test after job 74 BO plus 0 BWPD.

1%" treating string and tail pipe movement.

Sanded up after beivrz g brought in at80 BO plus 0B P What is claimed is: l. A process for forming a resin-consolidated sandturbulence near the end of the conduit through which the slurry is displaced.

5. The process of claim 1 in which said slurry is injected at a substantially constant rate and said indications of decreases in injectivity comprise surges in a pressure required to sustain said rate.

6. A process for treating a cased and perforated interval of a well by sandpacking the well with grains that are coated with a self-curing epoxy resin formulation and suspended in a liquid hydrocarbon, comprising:

pumping said suspension of grains into the well through a conduit having a point of discharge near the lowest of said perforations; raising said point of discharge each time the height of masses of sand deposited within said casing and perforations have reached said point of discharge so that the point of discharge is reached at each of a succession of depths between the depths of the lowest'and highest of said perforations;

terminating the inflowing of the suspension when the mass of sand extends above the highest of said perforations;

allowing said resin formulation to cure and consolidate said deposited masses of sand grains; and drilling out sand that was consolidated within the casing.

7. The process of claim 6 in which said cased and perforated interval is one through which fluid and sand have been produced and the amount of suspension that is pumped into said well is sufficient to repack voids in the reservoir with a deposited mass of coated sand grains.

8. The process of claim 6 in which said suspension is injected at a substantially constant rate so that when the heights of said deposited masses of sand grains have reached the discharge point, a surface indication is provided by the increased injection pressure required to maintain the constant rate of inflow.

9. The process of claim 6 in which said suspension is pumped into the perforated interval at a rate that creates turbulence near said point of discharge.

10. The process of claim 6 in which said epoxy resin formulation is a solution of epoxy resin-forming material and amino group containing curing agent dissolved in liquid polar organic solvent and said grain suspending liquid is a liquid hydrocarbon having limited miscibility with said polar organic solvent. 

2. The process of claim 1 in which said sand grains are coated with a solution of epoxy resin-forming material and amino group containing curing agent dissolved in liquid polar organic solvent and the so-coated grains are suspended in liquid hydrocarbon having a limited miscibility with said polar organic solvent.
 3. The process of claim 1 in which from about eight to 10 100 pound sacks of coated sand grains are used per foot of perforation through which sand has previously been produced.
 4. The process of claim 1 in which said slurry is displaced into the perforated interval at a rate that creates turbulence near the end of the conduit through which the slurry is displaced.
 5. The process of claim 1 in which said slurry is injected at a substantially constant rate and said indications of decreases in injectivity comprise surges in a pressure required to sustain said rate.
 6. A process for treating a cased and perforated interval of a well by sandpacking the well with grains that are coated with a self-curing epoxy resin formulation and suspended in a liquid hydrocarbon, comprising: pumping said suspension of grains into the well through a conduit having a point of discharge near the lowest of said perforations; raising said point of discharge each time the height of masses of sand deposited within said casing and perforations have reached said point of discharge so that the point of discharge is reached at each of a succession of depths between the depths of the lowest and highest of said perforations; terminating the inflowing of the suspension when the mass of sand extends above the highest of said perforations; allowing said resin formulation to cure and consolidate said deposited masses of sand grains; and drilling out sand that was consolidated within the casing.
 7. The process of claim 6 in which said cased and perforated interval is one through which fluid and sand have been produced and the amount of suspension that is pumped into said well is sufficient to repack voids in the reservoir with a deposited mass of coated sAnd grains.
 8. The process of claim 6 in which said suspension is injected at a substantially constant rate so that when the heights of said deposited masses of sand grains have reached the discharge point, a surface indication is provided by the increased injection pressure required to maintain the constant rate of inflow.
 9. The process of claim 6 in which said suspension is pumped into the perforated interval at a rate that creates turbulence near said point of discharge.
 10. The process of claim 6 in which said epoxy resin formulation is a solution of epoxy resin-forming material and amino group containing curing agent dissolved in liquid polar organic solvent and said grain suspending liquid is a liquid hydrocarbon having limited miscibility with said polar organic solvent. 